1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and particularly to generation of a color separation table used in conversion of an image signal into a signal of quantity of color material such as ink or toner.
2. Description of the Related Art
As one of methods of generating this kind of color separation table, a method using a colorimetry value of a patch on a predetermined lattice point has been known. For example, regarding lattice points on predetermined lines connecting vertexes of a cube defined in RGB space, on the basis of the colorimetry value of the patch, lattice point data (color separation data) is obtained. Regarding other lattice points which do not exist on these lines, lattice point data is obtained by interpolation using the lattice point data of the lattice points on the predetermined lines (Japanese Patent Application Laid-open No. 2003-116016). In the interpolation in this method, the above cube is divided into six tetrahedrons having the above lines as their sides, and further, in each tetrahedron, plural triangles parallel to one triangle of the tetrahedron are defined, whereby two-dimensional interpolation is performed for the respective triangles. This interpolation provides lattice point data of lattice points inside its triangle.
In this method, generally, after interpolation processing, smoothing processing is performed for the lattice point data. For example, smoothing of filtering by use of a low pass filter is performed. Hereby, such an adverse effect can be reduced that change of the lattice point data becomes discontinuous in a boundary between these interpolation areas due to the interpolation performed for each tetrahedron. Then, printing is performed based on the lattice point data of a table generated by such the processing, and a printed image can be prevented from having a false contour generated due to the above discontinuity.
FIG. 15 is a flowchart showing the above-described conventional table generating processing. In FIG. 15, firstly, in a step S151, regarding lattice points of a W-K line, each line of W-C, M, Y, R, G, B, each line of C, M, Y, R, G, B-K, and each line of M-R, R-Y, Y-G, G-C, C-B, B-M, which connect vertexes of a cube defined in RGB space, color separation data are obtained. Namely, a color separation table for the above each line is generated.
Next, in a step S152, internal interpolation processing is performed, using the obtained lattice point data on each line, whereby color separation data is obtained for lattice points in portions other than the above line. In a step S153, smoothing processing is performed for the obtained color separation data, and the table generation processing ends.
Thus, performing smoothing processing allows distortion of the color separation table caused by obtaining the color separation data in the interpolation processing for each of the plural areas obtained by dividing the cube, and distortion caused by the internal interpolation processing, to be removed. As a result, it can be suppressed that the false contour is produced in an image printed on the basis of the color separation data obtained by this color separation table.
The color separation table is generated basically on the basis of the color-measured patch. Further, it has been also known that lattice point data is so determined as to control the quantity of the color material in consideration with attachment property of the color material onto a printing medium such as paper, for example, ink absorbency in case that the color material is ink. For example, the maximum quantity of ink which the printing medium of the predetermined area can absorb is previously obtained, and the color material quantity of each color which is the above-obtained lattice point data is corrected so as not to exceed the obtained maximum quantity. In this case, if the color material quantity correction processing is performed without taking the above smoothing processing into consideration, the result by the smoothing processing is impaired by the correction processing, so that such an adverse effect may be produced that the false contour is conspicuous in a printed image. Alternatively, limiting of the color material quantity is not enough, so that bleeding of ink may occur in the printed image.